WO2024014804A1 - Method for recovering rare earth metal - Google Patents

Abstract

The present disclosure describes an eco-friendly bio-based process for effectively recovering a rare earth metal from a rare earth metal source, particularly a low-grade phosphate mineral such as monazite, through solvo-chemical extraction.

Description

Recovery method of rare earth metals

This disclosure relates to methods for recovery of rare earth metals. More specifically, the present disclosure relates to an environmentally friendly, bio-based process for effectively recovering rare earth metals from rare earth metal sources, particularly low-grade phosphate minerals such as monazite, through solvo-chemical extraction.

Rare earth metals (REM) are widely used in advanced manufacturing industries such as semiconductors due to their unique physical and chemical properties such as high chemical stability and thermal conductivity, and demand is currently rapidly increasing worldwide. In particular, rare earth metals are mainly applied to catalysts, ceramics and glass, metals and alloys, and abrasives, and among them, cerium (Ce) is known to be used in the largest amount among the rare earth metals.

Meanwhile, rare earth metals do not exist in elemental form in nature, but are produced as various minerals. Rare earth-containing minerals exist in the form of halides, carbonates, oxides, and phosphates. do. Currently, approximately 200 types of minerals are known to contain rare earth elements, but most of them contain small amounts of rare earth metals, so the number of mineral species that can be used industrially is limited.

In this regard, three types of major rare earth minerals can be exemplified: bastnsite, monazite, and xenotime, of which monazite is a cerium (Ce) group rare earth metal in phosphate form. It is a mineral that exists in abundance and is distributed in many areas around the world.

In addition, monazite has chemical stability, so in order to recover rare earth metals, it is used for concentration (WO 2016-109966 A1), smelting (WO 2009-021389 A1), and leaching after acid and alkali decomposition - ion exchange (Korean Patent Publication No. 2013). -0076261), hydrochloric acid leaching (US Patent No. 9752213), mechanochemical leaching (Domestic Patent No. 1058567), biological leaching (Domestic Patent No. 1641074), solvent extraction (Chinese Patent No. 101319275), etc. Methods are known, but acid or alkaline decomposition methods are mainly applied.

Among the above-mentioned methods, the acid decomposition method is advantageous in that it uses a low-cost acid such as sulfuric acid, but it can cause corrosion of equipment and emit a large amount of corrosive gas, causing environmental pollution. On the other hand, alkaline decomposition method is relatively simple to operate and has advantages in terms of decomposition rate, but is expensive and may cause environmental pollution. Moreover, the acid or alkali decomposition method has the problem of consuming a large amount of energy and also consuming a large amount of reagents to neutralize the free acid or alkali remaining after leaching of the roasted sample.

As an alternative, bio-based technologies using recovery methods using microorganisms, such as biosorption, bioleaching and biomineralization, are known. However, these studies mainly focus on the solubilization of phosphate in rare earth minerals using phosphate solubilizing microorganisms rather than the leaching of rare earth metals (Korean Patent No. 1641074).

As such, there is a need for an environmentally friendly and effective method of separating and recovering rare earth metals from low-grade resources (or minerals), specifically phosphate minerals such as monazite, overcoming the limitations of the above-described prior art.

One embodiment of the present disclosure seeks to provide an environmentally friendly integrated process capable of selectively leaching or eluting rare earth elements from low-grade rare earth-containing phosphate sources such as monazite using microorganisms, and then implementing effective separation and recovery.

According to the first aspect of the present disclosure,

a) While culturing phosphorus-soluble microorganisms with a solid rare earth metal-containing phosphate source, phosphorus in the rare earth metal-containing phosphate source is leached by metabolic acid released from the microorganisms to form a phosphorus-containing leachate and phosphorus-containing phosphate source. forming a depleted residue, the rare earth metal-containing phosphate source comprising: (i) cerium, (ii) at least one rare earth metal other than cerium, and (iii) iron;

b) Microorganisms with sulfur and iron oxidation capabilities are cultured with the phosphorus-depleted residue, and iron in the phosphorus-depleted residue is leached by a metabolic leaching agent released from the microorganisms with sulfur and iron oxidation capabilities to produce iron. - forming a depleted residue;

c) treating the iron-depleted residue with acid to leach rare earth metals and selectively oxidize cerium(III) among the rare earth metals to convert it to cerium(IV);

d) extracting cerium(IV) in the leachate obtained in step c) with an organic solvent to form a cerium-rich extract and a cerium-depleted raffinate; and

e) recovering cerium from the extract;

A method for recovering rare earth metals containing a is provided.

According to an exemplary embodiment, the rare earth metal-containing phosphate source may contain 0.05 to 0.6 weight percent phosphorus (P) on an elemental basis.

According to an exemplary embodiment, the rare earth metal-containing phosphate source comprises, on an elemental basis, 0.5 to 4% by weight cerium, 0.1 to 3.5% by weight of at least one rare earth metal other than cerium, and 5 to 30% by weight of May contain iron.

According to an exemplary embodiment, the rare earth metal-containing phosphate source may include up to 25% by weight of other metals in oxide form.

According to an exemplary embodiment, the rare earth metal-containing phosphate source may be monazite.

According to an exemplary embodiment, the rare earth metal-containing phosphate source in step a) may be in the form of particles or pulverized particles with a size ranging from 50 to 400 mesh.

According to an exemplary embodiment, the rare earth metal other than cerium may include at least one of lanthanum (La) and yttrium (Y).

According to an exemplary embodiment, the other metal may include at least one selected from the group consisting of silicon, titanium, aluminum, zirconium, sodium, potassium, calcium, manganese, and magnesium.

According to an exemplary embodiment, the metabolic acid in step a) includes oxalic acid, and the concentration of oxalic acid in the metabolic acid may be at least 200 mM.

According to an exemplary embodiment, in step a), some of the rare earth metals in the phosphate source may be precipitated in the form of organic salts by metabolic acid and contained in the residue.

According to an exemplary embodiment, the culture in step a) is performed in the presence of microorganisms initially cultured in a growth medium, where the liquid/S ratio of the growth medium/phosphate source is adjusted in the range of 5 to 15. It can be.

According to an exemplary embodiment, step b) is performed using a medium supplemented with sulfur and nutrients, where the ratio of medium/liquid ratio of phosphorus-depleted residue may be adjusted in the range of 2 to 5.

According to an exemplary embodiment, the acid in step c) is nitric acid, which may involve ozone-nitration treatment.

According to an exemplary embodiment, the organic solvent in step d) may include a water-immiscible organic phosphorus compound.

According to an exemplary embodiment, the concentration of the organic phosphorus compound in step d) is in the range of 0.05 to 0.5 M, and the volume ratio of the organic phase/water phase (O/A) is in the range of 5:1 to 1:5. It can be adjusted.

According to an exemplary embodiment, step e) converts cerium (IV) to cerium (III) using hydrogen peroxide as a reducing agent, and then strips cerium (III) with an acid solution to obtain a cerium-containing acid solution. there is.

According to an exemplary embodiment, f) recovering rare earth metals other than cerium from the raffinate may be further included.

According to an exemplary embodiment, the cerium contained in the acid solution through the stripping may be recovered by precipitating it in the form of cerium oxalate by oxalate ions.

According to an exemplary embodiment, the rare earth metal other than cerium in the raffinate may include at least one of lanthanum (La) and yttrium (Y).

According to an exemplary embodiment, step f) may include precipitating rare earth metals other than cerium in the raffinate in the form of oxalate by oxalate ions.

The rare earth metal recovery process according to an embodiment of the present disclosure is a bio-based process using microorganisms, which recovers phosphate from rare earth metal sources such as low-grade minerals such as monazite without the use of heat treatment or highly concentrated chemicals that are involved in the prior art. It provides an eco-friendly and sustainable solution by effectively destroying the structure to separate and recover rare earth metals. In particular, it can be environmentally friendly, low energy-intensive, and highly efficient, and fits the ESG strategy of rare earth-related companies, so widespread commercialization is expected in the future.

Figure 1 schematically shows an example of an integrated process for separating and recovering phosphorus (P), iron (Fe), cerium (Ce), and rare earth metals other than cerium (La, Y) from a solid rare earth metal-containing phosphate source. It is a drawing showing;

Figure 2 is a graph showing the production concentration and bioleaching rate of metabolic acids over time during the leaching step of phosphorus (P) in a rare earth metal-containing phosphate source using microorganisms in an example;

Figure 3 shows the leaching amount and bioleaching rate of iron over time during the leaching step of iron (Fe) in the phosphorus-depleted residue after separation of phosphorus (P) in the rare earth metal-containing phosphate source using microorganisms, respectively. It is a graph;

Figure 4 is a graph showing the leaching rates of each of the three rare earth metals (Ce, La and Y) according to the concentration of nitric acid as a result of ozone-nitration treatment of the iron-depleted residue after separation of iron (Fe). ;

Figure 5 is a graph showing the extraction rates of three rare earth metals (Ce, La, and Y) in the leachate according to the concentration of the organic extractant;

Figure 6 is a graph showing the cerium stripping rate according to the hydrochloric acid concentration during the step of performing hydrochloric acid stripping using hydrogen peroxide (concentration: 0.1 mol/L) on the cerium(IV)-containing extract;

Figure 7 is an XRD pattern for cerium oxalate precipitate formed by reaction with oxalate ions after stripping;

Figure 8 shows the precipitation rate of rare earth metals according to the concentration of oxalate ions during the process of forming precipitates (oxalate precipitates) of rare earth metals (La, Y) other than cerium by adding ammonium oxalate to raffinate produced by cerium extraction. It is a graph representing; and

Figure 9 is an XRD pattern for an oxalate mixed precipitate of rare earth metals (La, Y).

The present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. In addition, the attached drawings are intended to aid understanding, and the present invention is not limited thereto, and details regarding individual configurations can be appropriately understood based on the specific purpose of the related description described later.

Terms used in this specification may be defined as follows.

“Rare earth metals” is a general term for 17 types of elements including scandium, yttrium, and 15 elements of the lanthanide series with atomic numbers from 57 to 71, which are group 3A of the periodic table. Their chemical properties are similar to each other, and generally all have +3. It exists in a form with an oxidation number. In addition, rare earth metals can generally be divided into light rare earth metals (elements) and medium rare earth metals (elements), and the four elements from lanthanum (La) with atomic number 57 to neodymium (Nd) with atomic number 60 are light. While they belong to rare earths, the remaining 13 elements can be understood as belonging to medium rare earths.

“Bioleaching” may generally refer to a process of dissolving a metal from a mineral source by microorganisms, and specifically to a process of converting a solid metal to a water-soluble form.

“Culture medium” may refer to an aqueous solution of nutrients available for cell growth.

“Phosphate solubilizing microorganism (PSM)” may refer to a microorganism that converts immobilized phosphorus into water-soluble phosphorus.

“Extraction” can mean transferring a particular component, specifically a metal, from one phase to another.

“Stripping” may refer to a process of separating or removing a specific metal from a liquid medium or solvent, and selective stripping may refer to a process of separating or removing a specific metal from a liquid medium or solvent containing a plurality of metals. can do.

In this specification, when a numerical range is specified as a lower limit and/or an upper limit, it can be understood that any subcombination within the numerical range is also disclosed. For example, when written as “1 to 5,” it can include 1, 2, 3, 4, and 5, as well as any sub-combinations therebetween.

When any component or member is described herein as being “connected to” another component or member, unless otherwise stated, it refers not only to being directly connected to said other component or member, but also to the other component or member. Alternatively, it may be understood that cases of being connected through the intervention of a member are also included.

Similarly, the term “contact” may also be understood to include not only direct contact, but also contact through the intervention of other components or members.

When it is said to “include” a certain component, this means that it may further include other components, unless otherwise specified.

According to one embodiment of the present disclosure, a process of bioleaching and solvo-chemical extraction using microorganisms is provided to separate and recover rare earth metals from rare earth metal-containing phosphate sources, from which An exemplary process for separating and recovering phosphorus (P), iron (Fe), cerium (Ce), and rare earth metals other than cerium (La, Y) is shown in FIG. 1.

Referring to the drawing, a solid rare earth metal source is provided as a starting material, and in the illustrated embodiment, it may be a phosphate source containing cerium and rare earth metals other than cerium and additionally containing iron. Typically, it may be a naturally occurring low-grade mineral. As an example, the rare earth metal source may be a mineral, specifically monazite. Monazite may be a phosphate mineral generally represented by chemical formulas such as (Ce,La,Th)PO ₄ and (Ce,La,Nd,Th)PO ₄ .

In the rare earth metal source, the content of phosphorus (P), on an elemental basis, is for example about 0.05 to 0.6% by weight, specifically about 0.07 to 0.3% by weight, more specifically about 0.09 to 0.2% by weight, especially specifically It may be around 1% by weight.

Meanwhile, the content of cerium (based on element) in the rare earth metal salt source is, for example, about 0.5 to 4% by weight, specifically about 0.5 to 3% by weight, more specifically about 0.7 to 2% by weight, particularly specifically 1% by weight. It may be nearby. Additionally, rare earth metals other than cerium include lanthanum (La) and yttrium (Y), and may contain at least one of these. However, this specific example is not limited to this, and it can be understood that other rare earth metals (for example, Pr, etc.) may be contained instead of or in addition to lanthanum and/or yttrium. As an example, the content (based on element) of rare earth metals other than cerium may range, for example, from about 0.1 to 3.5% by weight, specifically from about 0.3 to 2% by weight, and more specifically from about 0.5 to 1% by weight. . Additionally, the iron content (on an elemental basis) in the rare metal source may range, for example, from about 5 to 30 wt%, specifically from about 8 to 20 wt%, and more specifically from about 10 to 15 wt%.

According to an exemplary embodiment, when the rare earth metal source is in mineral form, it may additionally contain other metals in addition to the above-described phosphorus, rare earth metals, and iron, and these other metals are not particularly limited and include, for example, silicon. , titanium, aluminum, zirconium, sodium, potassium, calcium, manganese, magnesium, etc. The content of other metals may be, for example, up to about 25% by weight, specifically about 10 to 20% by weight, and more specifically around 20% by weight, based on oxide.

The content of individual components in the above-described rare earth metal source may be understood as illustrative, and may vary depending on the production area, etc.

In this regard, an exemplary composition of monazite available from a specific origin as a rare earth metal source can be shown (% by weight) in Table 1 below.

Fe2O3 _	Al 2 O 3	SiO 2	TiO 2	Y 2 O 3	La 2 O 3	CeO 2	PO 4	Na 2 O	MgO	K2O	MnO	CaO	ZrO2
28.4	8.1	34.7	11.3	0.13	0.68	1.06	0.86	0.8	1.6	1.3	0.6	5.1	5.7

According to an exemplary embodiment, the solid rare earth metal-containing phosphate source may be in the form of ground or particles so that subsequent leaching (bioleaching) can be carried out effectively. At this time, the size of the pulverized material or particles may be determined by considering the sieving results, for example, it may be in the range of about 50 to 400 mesh, specifically about 70 to 350 mesh, and more specifically about 80 to 325 mesh. there is.

Meanwhile, in the case of minerals such as monazite, grinding means known in the art can be used. As an example, the grinding means may be a roller grinder, vibrating mill, ball mill, pot mill, hammer mill, pulverizer, gyratory mill, etc., but is not limited thereto.

Bioleaching of phosphorus (P)

Referring to Figure 1, the phosphate source undergoes a bioleaching step in which phosphorus is leached using phosphorus-soluble microorganisms.

As shown, the reason for preferential leaching and separation of phosphorus (P) before other components or elements from rare earth metal-containing phosphate sources, especially monazite, can be explained as follows: In monazite, phosphate is a host of rare earth metals. Acting as a matrix, the rare earth metal remains in the center with a distorted coordination sphere surrounded by eight oxides of phosphate. Therefore, in order to leach rare earth metals with a lixiviant, it may be advantageous to first destroy the phosphate structure.

In the depicted embodiment, in the case of phosphorus-soluble microorganisms (PSM), the metabolic acids produced upon incubation with the aforementioned phosphate source act as a leaching agent, converting the phosphorus in the phosphate source to a soluble form, thereby allowing it to leach out. Can be selected from available types. As an example, the phosphorus-soluble microorganism may be at least one selected from the group consisting of Aspergillus genus and Penicillium genus. In addition, various penicillium species, heterotrophic bacterial species, etc. can be used, examples of which include Pseudomonas rhizosphaerae, Pseudomonas putida, Pseudomonas fluorescens, Bacillus megaterium, Paenibacillus polymyxa, Ensifer meliloti, and Azospirillum brasilense. , Mesorhizobium ciceri, Acetobacter aceti, Pseudomonas aeruginosa, etc., and can be used alone or in combination. However, the types listed above may be understood as illustrative purposes.

Phosphorus (P) is an essential element for life, maintaining major cellular reactions, metabolic processes of carbon and amino acids, and is essential for ATP, enzyme reactions, and energy transfer. At this time, the phosphorus-soluble microorganism can discharge insoluble phosphorus in the phosphate source in a soluble form through acidification, chelation, exchange reaction, etc.

According to an exemplary embodiment, for culturing phosphorus-soluble microorganisms, the medium may be a growth medium, specifically a modified growth medium, wherein the phosphate source is combined with the microorganisms being initially cultured in the growth medium, and then the microorganisms are grown. It can be processed by culturing. As an example, the culture of microorganisms may be performed in a fed-batch culture method. “Fed-batch culture” means that at least one nutrient (e.g., sucrose) is added to the reactor intermittently or continuously during the culture process. It may mean a process that is added. As an example, the concentration of microbial spores in the initial growth medium may be, for example, at least about 3×10 ⁶ spores/mL, specifically about 3×10 ⁸ to 3×10 ¹⁰ spores/mL, more specifically about It may be 1×10 ⁹ to 5×10 ⁹ spores/mL, particularly around 3×10 ⁹ spores/mL, but this may be understood as an example. At this time, since the phosphorus component in the phosphate source functions as a source that provides phosphorus necessary for culture, separate supply of phosphorus may not be required. Since the components of the medium used for microbial growth in this embodiment are known in the art, separate detailed description will be omitted. Meanwhile, in an exemplary embodiment, the liquid-to-liquid ratio (L/S ratio) of growth medium/phosphate source (solid phase) can be adjusted considering the amount of medium and phosphate source, for example, about 5 to 15, specifically It may be about 5 to 13, more specifically about 8 to 12, and especially about 10.

As the cultivation time of the microorganism increases, the amount of metabolic acid produced increases, and as a result, phosphorus in the phosphate source is leached. An exemplary reaction involved in this leaching process can be expressed as shown in Scheme 1 below.

[Scheme 1]

REM(PO ₄ ) + n[HA] = REMA _n + H _n PO ₄

According to an exemplary embodiment, the metabolic acid produced by the microorganism may include, for example, oxalic acid (C ₂ H ₂ O ₄ ), and may additionally be selected from gluconic acid, citric acid, formic acid, butyric acid, maleic acid, etc. It may contain at least one. In this regard, the concentration of metabolic acid produced by the microorganism may be, for example, at least about 200mM, specifically about 230 to 1200mM, more specifically about 500 to 900mM, especially specifically about 840mM, , At this time, the proportion of oxalic acid may be, for example, at least about 35%, specifically about 40 to 80%, more specifically about 50 to 70%, and especially specifically about 56%, based on the mole of the total metabolic acid. there is. Exemplarily, the concentration of oxalic acid among the metabolic acids produced by microbial culture is, for example, at least about 200 mM, specifically about 300 to 900 mM, more specifically about 350 to 600 mM, and particularly specifically around about 470 mM. It can be.

In an exemplary embodiment, the conditions for bioleaching of the phosphorus component are not particularly limited because they may vary depending on the composition and properties of the phosphate source, which is the starting material, but the temperature is, for example, about 20 to 45 (±1). ℃, specifically about 25 to 40 (±1) ℃, more specifically about 30 to 35 (±1) ℃, especially specifically can be adjusted around 30 (±1) ℃, and the pH is, for example For example, it may be adjusted in the range of about 4 to 7, specifically about 4.5 to 6.5, and more specifically about 5 to 6. Additionally, leaching of phosphorus components may be performed under stirred or non-stirred conditions, but it may be advantageous to carry out the leaching under stirred conditions. In addition, the leaching time may be set within a range of, for example, about 2 to 20 days, specifically about 3 to 14 days, more specifically about 3 to 12 days, and particularly about 8 to 10 days. It is not limited.

In an exemplary embodiment, through the bioleaching process using the phosphorus-soluble microorganisms described above, at least about 70%, specifically at least about 75%, and more specifically about 80 to 90% of the total elemental phosphorus (P) in the phosphate source. %, specifically about 83%, can be solubilized.

In addition, in the process of bioleaching of phosphorus components by metabolic acid, not only phosphorus (P) but also one or two or more other components in the rare earth metal-containing phosphate source may be leached or eluted at least in part. Components that are additionally leached in this way may be alkali metals (e.g., sodium, potassium, etc.), alkaline earth metals (e.g., calcium, etc.), rare earth metals, iron, etc. However, the amount of each component leached (or eluted) together with phosphorus (P) may vary depending on the composition of the phosphate source, etc., and is not limited to a specific range.

In addition, rare earth metals leached together with phosphorus can form complexes by combining with metabolic acids, and can be converted from inorganic (oxide) form to organic form (e.g., rare earth oxalate), and these organic substances or organic salts are It may precipitate and become incorporated into the phosphorus-depleted residue, or it may be submitted together for subsequent processing. Examples of precipitation reactions of rare earth metals (when converted to oxalate salts) can be represented as shown in Schemes 2 and 3 below.

[Scheme 2]

2Ce ³⁺ + 3C ₂ O ₄ ^2- → Ce ₂ (C ₂ O ₄ ) ₃

[Scheme 3]

2(La ³⁺ ,Y ³⁺ ) + 3C ₂ O ₄ ^2- → (La,Y) ₂ (C ₂ O ₄ ) ₃

Meanwhile, according to an exemplary embodiment, the phosphorus in the leachate can be obtained in the form of a solution containing high purity phosphorus through an additional separation and purification process. As a method for separating and purifying phosphorus, a solvo-chemical method, specifically extraction and stripping using an organic solvent as shown, can be applied. At this time, as an extractant, for example, one or more organic solvents selected from phosphine oxide compounds having a long carbon skeleton (about 16 to 48 carbon atoms, specifically about 25 to 35 carbon atoms) can be used. A phosphorus-rich extract is generated by this. Thereafter, a solution containing high purity phosphorus can be obtained by adding a stripping solution selected from at least one inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, etc. to the phosphorus-rich extract. Additionally, the organic solvent in the extract can be recycled and reused as an extractant in the extraction step before the stripping step.

According to an exemplary embodiment, the extraction conditions are not particularly limited, but the volume ratio of organic phase to aqueous phase is about 1:5 to 5:1, specifically about 1:3 to 3:1, more specifically about 1:2. It can be adjusted in the range of 2:1. Additionally, the concentration of the extractant (based on the organic phase) may be, for example, around 0.1 to 0.5 M, specifically around 0.15 to 0.4 M, more specifically around 0.2 to 0.3 M, and particularly specifically around 0.25 M. Meanwhile, the equilibration time may be, for example, about 1 to 30 minutes, specifically about 2 to 20 minutes, more specifically about 4 to 10 minutes, and particularly about 5 minutes. The extraction temperature may be, for example, about 20 to 40° C., specifically about 22 to 35° C., more specifically about 24 to 30° C., and particularly specifically about 25° C. In addition, the phase separation time may be, for example, For example, it may be set to about 5 to 30 minutes, specifically about 7 to 25 minutes, more specifically about 9 to 15 minutes, and particularly about 10 minutes.

According to an exemplary embodiment, but not particularly limited, the volume ratio of organic phase to aqueous phase is about 1:5 to 5:1, specifically about 1:3 to 3:1, more specifically about 1:2 to 2:1. It can be adjusted in the range of 1. Additionally, the acid concentration may be, for example, about 1 to 3 M, specifically about 1.4 to 2.7 M, more specifically about 1.8 to 2.5 M, and especially specifically about 2 M. In addition, hydrogen peroxide may be used during stripping. At this time, the concentration of hydrogen peroxide may be, for example, about 0.05 to 0.2 M, specifically about 0.08 to 0.15 M, and more specifically about 0.1 M. The contact time may be, for example, about 1 to 20 minutes, specifically about 3 to 10 minutes, more specifically about 4 to 6 minutes, especially about 5 minutes. Meanwhile, the stripping temperature may be, for example, about 20 to 40° C., specifically about 22 to 35° C., more specifically about 24 to 30° C., and particularly specifically about 25° C. In addition, the phase separation time may be, For example, it may be set to about 5 to 30 minutes, specifically about 7 to 25 minutes, more specifically about 9 to 15 minutes, and particularly specifically about 10 minutes.

Bioleaching of iron (Fe)

Referring again to FIG. 1, bioleaching using microorganisms can be performed to separate and recover iron from the phosphorus-depleted residue (specifically, iron-rich residue) remaining after phosphorus leaching.

According to an exemplary embodiment, the microorganisms usable for iron leaching are microorganisms with sulfur and iron oxidation capabilities, from which a metabolic leaching agent is released. Such microorganism may be at least one selected from the group consisting of Alicyclobacillus genus and Sulfobacillus genus. Specifically, the Alicyclobacillus genus is a microorganism belonging to the Alicyclobacillaceae family and may be a Gram-positive or Gram-variable microorganism, examples of which include A. acidiphilus, A. disulfidooxidans, A. montanus, A. sacchari , etc. Additionally, microorganisms belonging to the Sulfobacillus genus include S ulfobacillus acidophilus, Sulfobacillus benefaciens, Sulfobacillus disulfidooxidans, Sulfobacillus sibiricus, Sulfobacillus thermosulfidooxidans, and Sulfobacillus thermotolerans .

In the depicted embodiment, the lixiviant formed as a metabolite during the cultivation of the microorganism may be sulfuric acid produced by the microorganism oxidizing elemental sulfur or sulfur in the presence of oxygen, as illustrated in Scheme 4 below. In this case, oxygen can be provided by external aeration.

[Scheme 4]

S + 1/2O ₂ + H ₂ O → SO ₄ ^2- + 2H ⁺

According to an exemplary embodiment, microorganisms for iron leaching can be cultured while supplementing or supplying sulfur and nutrients (e.g., scurose) to the remaining medium (spent medium) used in the above-described phosphorus leaching step. there is. At this time, the mechanism for leaching (solubilizing) iron from the phosphorus-depleted residue can be illustrated as shown in Scheme 5 below.

[Scheme 5]

0.5Fe ₂ O ₃ +2H ₂ SO ₄ → Fe(SO ₄ ) ₂ ^- + H ⁺ + 1.5H ₂ O

Illustratively, sulfur may be obtained from a variety of sources, such as biological sulfur that can be collected from a sedimentation tank at a wastewater treatment plant. In addition, as described above, organic acid ions (e.g., oxalate ions) that precipitate in the form of organic salts (e.g., oxalate salts) during the phosphorus leaching process and may exist in the residue serve as catalysts for the solubilization reaction of iron. It may work as a

According to an exemplary embodiment, the liquid ratio of medium/residue (phosphorus-depleted residue) during iron leaching can be adjusted considering the amount of medium and residue, for example, about 2 to 5, specifically It may range from about 2.3 to 4, more specifically about 2.5. In addition, the leaching conditions of iron in the phosphorus-depleted residue are not particularly limited because they can vary depending on various factors (iron content in the starting phosphate source, properties, etc.), but the temperature is, for example, about 30 to 60°C, more specifically around 40 to 55°C, specifically around 50°C, and the pH is, for example, around 1.1 to 2.8, specifically around 1.3 to 2, and more specifically around 1.5. It can be adjusted within the range of . Furthermore, leaching of iron may be performed under stirred or non-stirred conditions, but it may be advantageous to perform it under stirred conditions. In addition, the leaching time may be, for example, set in the range of about 1 to 21 days, specifically about 2 to 10 days, and more specifically about 4 to 8 days, but is not limited thereto.

In an exemplary embodiment, the amount of iron leached increases over time during the bioleaching step of iron, such that at least about 50%, specifically at least about 90%, and more specifically at least about 50% of the elemental iron in the phosphorus-depleted residue. At least about 99% can be solubilized and leached or eluted to form an iron-containing solution in the liquid phase and an iron-depleted residue as a solid component.

In addition, other components that are not completely removed during the phosphorus leaching process, such as alkali metals (eg, sodium, potassium, etc.) and alkaline earth metals (eg, calcium, etc.), may also be removed by leaching. However, leaching of rare earth metals may be limited, for example, less than about 2%, specifically less than about 1.5%, and more specifically less than about 1%.

In this way, the iron-containing solution produced by leaching of the phosphorus-depleted residue is separated separately, and the iron can be recovered through, for example, precipitation, solvent extraction, ion exchange, etc. Since this separation and recovery method is well known in the art, detailed description is omitted.

Separation and recovery of cerium

Referring to FIG. 1, a step of selectively separating and recovering cerium among rare earth metals in the iron-depleted residue may be performed.

Specifically, rare earth metals can be leached by treating the iron-depleted residue with acid (acid aqueous solution), and cerium(III) among the leached rare earth metals can be selectively oxidized and converted to cerium(IV).

According to an exemplary embodiment, nitric acid can be used as the acid for leaching rare earth metals. At this time, the concentration of the acid may be determined considering the cerium content, for example, about 0.2 to 8 M, specifically about 0.5 to 6 M, more specifically about 1 to 5 M, more specifically 2 to 4.5 M. , particularly specifically adjustable in the range of about 3 to 4 M. Typically, leaching of rare earth metals may tend to increase as the acid concentration increases.

Meanwhile, with the leaching of rare earth metals in the iron-depleted residue, cerium, which has an oxidation number of +3 among rare earth metals, that is, cerium(III), can be selectively oxidized to cerium(IV).

To oxidize leached cerium(III) to cerium(IV), for example, ozone, peroxydisulfate, oxygen, etc. can be used alone or in combination as an oxidizing agent, and specifically, ozone can be used. According to a specific embodiment, ozone-nitration treatment can be performed using nitric acid (nitric acid solution) and ozone, where the oxidation reaction can be performed according to Scheme 6 below.

[Scheme 6]

O ₃ + 2Ce ³⁺ + 2H ⁺ → 2Ce ⁴⁺ + H ₂ O + O ₂

In the above-described oxidation reaction, cerium is selectively oxidized, while the remaining rare earth metals (e.g., lanthanum and/or yttrium) remain with an oxidation number of +3. At this time, a catalyst that converts ozone into molecular oxygen can be used, and as an example, a catalyst bed containing CuO and MnO ₂ can be applied.

According to an exemplary embodiment, the liquid ratio of the acid/iron-depleted residue can be adjusted considering the amount of acid and residue, for example, about 2 to 20, specifically about 5 to 15, more specifically about It may range from 8 to 12, particularly around 10.

In addition, the conditions for leaching of rare earth metals and selective oxidation of cerium are not particularly limited, but the temperature is, for example, about 25 to 75 (±1) °C, specifically about 30 to 70 (±1) °C, more specifically. It can be adjusted around 45 to 60 (±1) °C, particularly around 55 (±1) °C. In addition, the processing time can be adjusted in the range of, for example, about 1 to 24 hours, specifically about 2 to 15 hours, more specifically 3 to 10 hours, and especially specifically about 4 to 6 hours, but this is for illustrative purposes. It can be understood as

According to an alternative embodiment, selective oxidation treatment of cerium may be performed by performing sulfuric acid (H ₂ SO ₄ ) leaching by sulfation roasting instead of ozone-nitration treatment. However, in this case, as a high concentration of acid is required, the ozone-nitration treatment described above may be advantageous.

As described above, as a result of leaching the rare earth metal with acid and selectively oxidizing cerium among the rare earth metals in the leach liquid, at least about 60%, specifically at least about 80%, of the cerium element in the iron-depleted residue. , more specifically, at least about 90% may be leached into the acid (acid solution). Additionally, of the leached cerium, at least about 80%, specifically at least about 85%, more specifically at least about 90%, especially specifically about 90.1% of the cerium (cerium(III)) having an oxidation number of +3 is +4. It can be oxidized to cerium (cerium(IV)), which has an oxidation number of . In addition, at least about 80%, specifically at least about 90%, and more specifically at least about 98% of the other rare earth (e.g., lanthanum and/or yttrium) elements in the iron-depleted residue may be leached.

Separation and recovery of cerium

Referring to FIG. 1, the steps of separating (extracting) and recovering cerium(IV) in the rare earth metal-containing acid leachate are performed.

In the illustrated embodiment, cerium(IV) can be separated from other rare earth metals with an oxidation number of +3 by using an organic solvent in the acid leachate, such as a water immiscible organophosphorus compound, as an extractant. there is. Representative examples of such organic phosphorus compounds are tri-alkyl phosphine oxide-based compounds, and at least one of these can be used. By way of example, an organophosphorus extractant is commercially available under the trade name Cyanex 923. Cyanex 923 is a mixture of four types of organic phosphine oxides, including dioctyl-monohexyl phosphine oxide (R'R2P=O; 31% by weight) and mono-octyl dihexyl phosphine oxide (R'2RP=O; 42% by weight). wt%), tri-hexyl phosphine oxide (R'3P=O; 14 wt%), and tri-n-octyl phosphine oxide (R3P=O; 8 wt%).

Meanwhile, during extraction, organic phosphorus compounds can be used while added or dissolved in a solvent, for example, an aromatic solvent. Such an aromatic solvent is a petroleum hydrocarbon series and may have 9 to 11 carbon atoms, specifically around 10 carbon atoms. From this, one type or two or more types can be used in combination. In addition, a phase modifier may be used together with the organic phosphorus compound. This phase modifier may be, for example, at least one selected from n-heptane, n-decanol, etc., and based on the organic phase, For example, it can be used in an amount of about 1 to 10 volume%, specifically about 3 to 8 volume%, and more specifically about 4 to 6 volume%. The composition of the above-described extractant may be understood as exemplary.

According to an exemplary embodiment, the concentration of the organic phosphorus compound during extraction (based on the organic phase) is adjusted, for example, in the range of about 0.05 to 0.5 M, specifically about 0.15 to 0.4 M, more specifically about 0.2 to 0.3 M. It may be possible, but it is not limited to this.

According to an exemplary embodiment, the volume ratio (O/A) of the organic phase/aqueous phase in the extraction step is, for example, about 5:1 to 1:5, specifically about 4:1 to 1:4, more specifically It may be in the range of about 3:1 to 1:3, specifically about 2:1, and considering the organic phosphorus compound composition and aqueous phase element distribution, it may be advantageous to adjust it within the above-mentioned range. Additionally, the extraction temperature is not particularly limited and may be, for example, about 10 to 40°C, specifically about 20 to 30°C, and more specifically, room temperature.

In this way, through the extraction treatment of the rare earth metal-containing leachate, at least about 95%, specifically at least about 98%, and more specifically at least about 99% of the cerium(IV) element in the leachate is extracted, while the other +3 is oxidized. The extraction of rare earth metals having a value may be, for example, about 5% or less, specifically about 4% or less, and more specifically about 3.5% or less. Therefore, most of the cerium(IV) is contained in the extract, while most of the remaining rare earth metals (specifically with an oxidation number of +3) remain in the raffinate.

According to the illustrated embodiment, as described above, a step of recovering cerium in high purity from a cerium-rich extract obtained by separating cerium (IV) by extraction can be performed.

Typically, recovery of cerium can be performed by converting (reducing) cerium (IV) back to cerium (III) and stripping cerium (III) using acid. At this time, the acid may be at least one inorganic acid selected from, for example, nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, etc. Exemplarily, the concentration of the acid may be determined considering the concentration of cerium (III), for example, about 0.2 to 3 M, specifically about 0.5 to 2.5 M, more specifically about 1 to 2 M. It may be a range, but this can be understood as an example. However, as the acid concentration increases, the stripping of cerium may tend to increase.

Meanwhile, hydrogen peroxide can be used as a reducing agent in a reductive stripping method for stripping cerium (IV) or Ce ⁴⁺ from the organic phase. Hydrogen peroxide is generally a strong oxidizing agent and can function as a strong reducing agent, and its standard potential values are shown in Schemes 7 to 9 below.

[Scheme 7]

Ce ⁴⁺ + e ^- ↔ Ce ³⁺ E ⁰ (Ce ⁴⁺ /Ce ³⁺ ) = 1.74 V

[Scheme 8]

O ₂ + 2H ^- + 2e ^- ↔ H ₂ O ₂ E ⁰ (O ₂ /H ₂ O ₂ ) = 0.693 V

[Scheme 9]

E ⁰ = E ⁰ (Ce ⁴⁺ /Ce ³⁺ ) - E ⁰ (O ₂ /H ₂ O ₂ ) = 1.74 - 0.693 = 1.047 > 0

From the above equation, hydrogen peroxide can be advantageous because Ce ⁴⁺ can be reduced to Ce ³⁺ and other metal impurities are not mixed during the reduction process. Ce ³⁺ formed by the reducing agent in this way can be stripped into the aqueous phase using an acid solution. According to an exemplary embodiment, the concentration of hydrogen peroxide may be set, for example, around 0.01 to 1 M, specifically around 0.05 to 0.5 M, more specifically around 0.08 to 0.2 M, and particularly specifically around 0.1 M. .

Through the above-described reduction stripping, at least about 60%, specifically at least about 90%, and more specifically at least about 95% of the cerium elements in the extract may be stripped, and as a result, a cerium aqueous solution may be formed. In order to recover cerium from the obtained cerium acid solution (aqueous solution), for example, an organic acid ion, specifically an oxalate ion (or oxalate ion) is supplied and reacted to precipitate an organic acid salt of cerium (specifically an oxalate salt). , specifically, it is possible to form a high purity cerium salt. As an example, the source of oxalate ions may include ammonium oxalate, oxalic acid, sodium oxalate, potassium oxalate, etc., and at least one of these may be used. At this time, the concentration of oxalate ions may be determined depending on the amount of cerium in the cerium aqueous solution, for example, about 0.002 to 2 M, specifically about 0.005 to 1 M, more specifically about 0.01 to 0.05 M, especially specifically It may range from about 0.02 to 0.03 M. However, the above numerical range may be understood as illustrative.

In addition, the temperature conditions for forming the precipitate are not particularly limited, but may be adjusted, for example, to a range of about 20 to 90°C, specifically about 50 to 85°C, and more specifically about 60 to 80°C.

Meanwhile, after stripping of cerium, the remaining organic phase, i.e. organic solvent, can be recycled and used as an extractant for cerium(IV) extraction in the front end.

Separation and recovery of rare earth metals other than cerium

Referring back to Figure 1, the raffinate separated from the extract during the extraction of cerium is in a cerium-depleted state and mainly contains rare earth metals other than cerium (specifically, rare earth metals with an oxidation value of +3). . According to an exemplary embodiment, the method may further include recovering rare earth metals other than cerium from the cerium-depleted raffinate.

At this time, for the purpose of recovering rare earth metals other than cerium contained in the raffinate, similar to the cerium recovery procedure, for example, organic acid ions, specifically oxalate ions (or oxalate ions) are supplied and reacted to produce rare earth metals. By forming a precipitate of an organic acid salt (specifically an oxalate salt) of (e.g., lanthanum and/or yttrium), high purity rare thorium metal can be recovered.

According to an exemplary embodiment, when forming a rare earth metal oxalate salt other than cerium, the concentration of oxalate ions is, for example, about 0.01 to 0.1 M, specifically about 0.02 to 0.07 M, more specifically about 0.03 to 0.05 M. It may be in the range of M. However, the above numerical range may be understood as illustrative. Additionally, the formation of the precipitate may be performed under elevated temperature conditions, for example, at a temperature controlled in the range of about 60 to 95°C, specifically about 65 to 90°C, and more specifically about 70 to 85°C.

In this way, through the precipitation process, at least about 50%, specifically at least about 80%, more specifically at least about 95% of the rare thorium (having an oxidation number of +3) elements such as lanthanum and/or yttrium in the raffinate, and Even about 98% can be obtained as precipitate (or coprecipitate). At this time, the obtained rare earth metal can be used as a precursor or catalyst precursor when producing a fluorescent material.

The present invention can be more clearly understood by the following examples, which are for illustrative purposes only and are not intended to limit the scope of the invention.

Example

go. matter

The materials used in this example are listed in Table 2 below.

substance name	manufacturing company
Glucose	ACS Reagent Chemicals
NaNO 3	Sigma-Aldrich
MgSO 4.7H 2 O	Sigma-Aldrich
KCl	Sigma-Aldrich
(NH 4 ) 2 SO 4	Sigma-Aldrich
K 2 HPO 4	Sigma-Aldrich
Yeast extract	Sigma-Aldrich
NaOH	Junsei Chemical Co. Ltd.
H 2 SO 4	Daejung
HCl	Daejung
HNO 3	Riedel-de-Haen
Organophosphorus compounds	Cyantec. Inc. Canada, Solvay
TBP	Sigma-Aldrich
Isododecanol	Shanghai Chemicals
C10	Shanghai Chemicals
H 2 O 2	Merck
C 2 H 8 N 2 O 4	Sigma Aldrich

me. Analysis method

The analysis performed in this example was performed as follows.

- The XRD pattern was analyzed using X'pert PRO PANalytical.

- The content of metal elements in the aqueous phase or organic phase was analyzed by inductively coupled plasma-stimulated emission spectroscopy using iCAP 7400 Duo (Thermo Scientific, USA).

Example 1

Vein-deposit monazite ore with the composition shown in Table 1 was ground to a mesh size of 80 to 325 by a ball mill, and phosphorus was bioleached as shown in FIG. 1. At this time, a mixed species of A. japonicus, A. aculeatus, A. niger, P. cinnamopurpureum, P. , and chrysogenum was used as the phosphorus-soluble microorganism.

Bioleaching was performed by introducing 100 g of monazite ore sample into a 1.5 L capacity bioreactor at a constant stirring speed of 200 rpm and an operating temperature of 30 °C. At this time _, the initially cultured microorganisms ( ³ It consisted of _4. ·7H ₂ O, 0.52 g/L KCl, and 1.6 g/L yeast extract.

Monazite ore, the only source of phosphate, was added by adjusting the liquid-to-liquid ratio (medium: ore) to 10. Initially, the pH of the medium was adjusted to 4.5 (using 5 wt% dil. H ₂ SO ₄ ). After 48 hours of incubation, the pH was adjusted back to 6.0 (using 5 wt% dil. NaOH) and maintained during the microbial treatment process. For accuracy, experiments were repeated at 24-hour intervals for a total of up to 14 days.

The production concentration and bioleaching rate of metabolic acid over time during the phosphorus leaching process for the monazite sample are shown in Figure 2.

According to the figure, the production of metabolic acids was negligible until day 3, indicating that no significant concentration of phosphorus was observed in the solution. However, at 9 days after microbial treatment, approximately 840 mM organic acids (metabolic acids), including 470 mM oxalic acid, 300 mM gluconic acid, and 70 mM citric acid, were produced, which remained largely unchanged until 14 days. There was no. Additionally, the production of organic acids increased rapidly in the period between 3 and 10 days, reaching >80%. Afterwards, the phosphorus leaching efficiency did not change significantly until 14 days and reached a level of 82.6%.

As such, there was no substantial change in the degree of phosphorus leaching in the sample even after prolonged contact with the organic acid in the solution, confirming that the microorganism passed the exponential growth stage, and no additional phosphorus was required as an energy source to maintain microbial growth. . Additionally, it was confirmed that in addition to phosphorus, 77% Na, 85% K, 81% Ca, 0.56% Y, 0.13% La, and 7.6% Fe were leached during the leaching process.

Example 2

After phosphorus leaching in Example 1, a second bioleaching was performed on the remaining residue. At this time, a metabolic leaching agent was produced through a biochemical reaction of microorganisms using spent medium, and the microorganisms used were a mixed species of the genus Alicyclobacilli and Sulfobacillus .

Additionally, the microorganisms were cultured in modified 9K medium, supplemented with biological sulfur (collected from the sedimentation tank of the wastewater treatment plant) and sucrose as energy sources at a temperature of 50 °C and aeration of external air at a flow rate of 0.5 L/min. did. The liquid/solid ratio (L/S ratio) was maintained at 2.5, and 1.0 L of metabolic leachable produced at pH 1.5 was used to contact 25 g of iron-rich residue obtained in Example 1 with the spent medium. Bioleaching was performed in a 1.5 L capacity bioreactor for 21 days under the conditions of a holding temperature of 50 °C and a stirring speed of 300 rpm. The leaching behavior of iron over time is shown in Figure 3.

According to the figure, 4 days after starting biological leaching, iron leaching reached more than 50%, and after 6 days, it reached about 90%. Iron leaching exceeding 99.8% occurred after 8 days. However, even as additional time elapsed, iron leaching of more than about 4848 mg/L was not observed (saturated state). The saturation state is believed to result from an increased pH value from an initial pH of 1.5 to a final pH of approximately 2.6. In addition to iron, most of Na, Ca and K ions were leached. However, La and Y were leached to less than about 2%.

Example 3

In order to leach rare earth metals (REM) in the iron-depleted residue obtained in Example 2, leaching was performed using a nitric acid solution in a closed container, and ozone-nitration treatment was additionally performed. As a result, the oxidation state of cerium was converted from Ce ³⁺ to Ce ⁴⁺ . At this time, the gas was injected into a catalytic cracker equipped with a catalyst layer of CuO and MnO ₂ that converts O ₃ into O ₂ . 20 g of the iron-depleted residue was leached with various concentrations of nitric acid solutions (0.5 to 4.0 mol/L HNO ₃ ) under the conditions of ozone supply and a liquid-to-liquid ratio of 10. Additionally, it was maintained for 4 hours at an O ₃ flow rate of 3.0 L/min and a temperature of 55°C. The leaching rates of each of the three rare earth metals (Ce, La, and Y) according to the concentration of nitric acid are shown in Figure 4.

Referring to the figure, when 0.5 mol/L HNO ₃ solution was used, the leaching of rare earth metals was very low. However, leaching of rare earth metals increased significantly at 1.0 mol/L HNO ₃ and reached its maximum value at 4.0 mol/L HNO ₃ . In particular, when 4.0 mol/L of HNO ₃ was used, more than 90% of Ce and more than 98% of Y and La were leached into the acid solution, and the concentrations of each rare earth metal in the leach solution were 1046 mg/L Ce ⁴⁺ , It was confirmed to be 688 mg/LY ³⁺ and 384 mg/L La ³⁺ .

Example 4

The leachate obtained using 3.0 mol/L of HNO ₃ in Example 3 contained 1025 mg/L of Ce ⁴⁺ , 682 mg/L of Y ³⁺ , and 372 mg/L of La ³⁺ , which was Solvo-chemical separation and rare earth metal recovery were performed.

Pre-mixtures of four organophosphorus compounds at various concentrations (0.05 to 0.25 mol/L) were pre-equilibrated to form water immiscible extractant media with different concentrations. In particular, the premixture of organophosphorus compounds contains 31% by weight of dioctyl-monohexyl P=O; 42% by weight mono-octyl dihexyl P=O; 14% by weight tri-hexyl P=O; and 8% by weight of trioctyl P=O were mixed with 5% by volume as a phase modifier and prepared in an aromatic solvent.

25 mL of rare earth metal leachate and 50 mL of water immiscible solvent mixture were contacted in a 100 mL glass separation funnel. For the solution equilibrated for 5 minutes at room temperature, both the aqueous and organic phases were separated for a settling time (10 minutes). The bottom settling aqueous stream as raffinate was collected, and the concentration of rare earth metals in the raffinate was analyzed after appropriate dilution. The extraction rates of three rare earth metals (Ce, La, and Y) in the leachate according to the concentration of the organic extractant are shown in Figure 5.

According to the figure, quantitative extraction of cerium in the leachate was achieved (approximately 99%) through a single extraction step using 0.25 mol/L extractant as the organic phase. On the other hand, the simultaneous extraction of lanthanum and yttrium was less than 3.5%. The rare earth metal with an oxidation value of +3 and the nitric acid loaded on the organic phase thus simultaneously extracted were separated by contact with water and scrubbing.

Example 5

Reduction stripping was performed on the Ce(IV)-containing extract (organic solvent) obtained in Example 4 using an aqueous hydrochloric acid solution (2.0 M), where H ₂ O ₂ was used as a reducing agent. (0.1 mol/L) was added.

50 mL of cerium-containing extract and 25 mL of aqueous hydrochloric acid solution were brought into contact in a 100 mL separation funnel. For the solution equilibrated for 5 minutes at room temperature, both the aqueous and organic phases were separated for a settling time (10 minutes). The bottom settling aqueous stream was collected as raffinate and the cerium concentration was measured after appropriate dilution. The cerium stripping rate according to the hydrochloric acid concentration (0.5 to 2.0 mol/L) during the step of performing hydrochloric acid stripping using H ₂ O ₂ (concentration: 0.1 mol/L) on the cerium-containing extract is shown in Figure 6.

Referring to the figure, it can be seen that the stripping of Ce(III) increased as the acid concentration increased, and up to 96.2% of cerium was stripped with 2.0 mol/L HCl. Additionally, when ammonium oxalate salt was added to the stripped solution, cerium oxalate was formed (see Figure 7).

Example 6

In Example 4, ammonium oxalate was added as a precipitating salt to 100 mL of raffinate produced after cerium extraction to precipitate La ³⁺ and Y ³⁺ . At this time, the precipitation conditions were set to a temperature of 90°C, a stirring speed of 150 rpm, and a contact time of 30 minutes, and about 98% of the rare earth metal with an oxidation value of +3 was deposited using 0.025 mol/L oxalate ions. Obtained. In this regard, the precipitation rate of rare earth metals (La, Y) other than cerium according to the concentration of oxalate ions during the formation of deposits (oxalate precipitates) is shown in Figure 8. Additionally, the XRD pattern for the oxalate mixed precipitate of rare earth metals (La, Y) is shown in Figure 9.

Referring to the figure, it can be seen that as the concentration of oxalate ions increases, the amount of precipitation of the oxalate salt of the rare earth mixture (La, Y) increases.

Simple modifications or changes of the present invention can be easily used by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (20)

1. a) While culturing phosphorus-soluble microorganisms with a solid rare earth metal-containing phosphate source, phosphorus in the rare earth metal-containing phosphate source is leached by metabolic acid released from the microorganisms to form a phosphorus-containing leachate and phosphorus-containing phosphate source. forming a depleted residue, the rare earth metal-containing phosphate source comprising: (i) cerium, (ii) at least one rare earth metal other than cerium, and (iii) iron;

   b) Microorganisms with sulfur and iron oxidation capabilities are cultured with the phosphorus-depleted residue, and iron in the phosphorus-depleted residue is leached by a metabolic leaching agent released from the microorganisms with sulfur and iron oxidation capabilities to produce iron. - forming a depleted residue;

   c) treating the iron-depleted residue with acid to leach rare earth metals and selectively oxidize cerium(III) among the rare earth metals to convert it to cerium(IV);

   d) extracting cerium(IV) in the leachate obtained in step c) with an organic solvent to form a cerium-rich extract and a cerium-depleted raffinate; and

   e) recovering cerium from the extract;

   A method for recovering rare earth metals comprising:
2. 2. The method of claim 1, wherein the rare earth metal-containing phosphate source contains 0.05 to 0.6 weight percent phosphorus (P) on an elemental basis.
3. 2. The method of claim 1, wherein the rare earth metal-containing phosphate source comprises, on an elemental basis, 0.5 to 4% by weight cerium, 0.1 to 3.5% by weight of at least one rare earth metal other than cerium, and 5 to 30% by weight iron. A method for recovering rare earth metals comprising:
4. 4. The method of claim 3, wherein the rare earth metal-containing phosphate source contains up to 25% by weight of other metals in oxide form.
5. 4. The method of claim 3, wherein the rare earth metal-containing phosphate source is monazite.
6. The method of claim 1, wherein the rare earth metal-containing phosphate source in step a) is in the form of particles or pulverized particles having a size ranging from 50 to 400 mesh.
7. The method of recovering rare earth metals according to claim 1, wherein the rare earth metals other than cerium include at least one of lanthanum (La) and yttrium (Y).
8. The method of claim 3, wherein the other metals include at least one selected from the group consisting of silicon, titanium, aluminum, zirconium, sodium, potassium, calcium, manganese, and magnesium.
9. The method of claim 1, wherein the phosphorus-soluble microorganism is at least one selected from the group consisting of Aspergillus genus and Penicillium genus, and

   A method for recovering rare earth metals, wherein the microorganism having the ability to oxidize sulfur and iron is at least one selected from the group consisting of Alicyclobacillus genus and Sulfobacillus genus.
10. The method of claim 1, wherein the metabolic acid in step a) includes oxalic acid, and the concentration of oxalic acid in the metabolic acid is set to at least 200 mM.
11. The method of recovering rare earth metals according to claim 1, wherein in step a), some of the rare earth metals in the phosphate source are precipitated in the form of organic salts by large acid and contained in the residue.
12. The method of claim 1, wherein the culturing in step a) is performed in the presence of microorganisms initially cultured in a growth medium, wherein the liquid-to-liquid ratio (L/S ratio) of the growth medium/phosphate source is adjusted in the range of 5 to 15. A method for recovering rare earth metals, characterized in that.
13. 2. The rare earth metal of claim 1, wherein step b) is performed using a medium supplemented with sulfur and nutrients, wherein the liquid ratio of the medium/phosphorus-depleted residue is adjusted in the range of 2 to 5. Recovery method.
14. The method of claim 1, wherein the acid in step c) is nitric acid and involves ozone-nitration treatment.
15. The method of claim 1, wherein the organic solvent in step d) includes a water-immiscible organic phosphorus compound.
16. The method of claim 15, wherein the concentration of the organic phosphorus compound is in the range of 0.05 to 0.5 M, and the volume ratio (O/A) of the organic phase/water phase is adjusted in the range of 5:1 to 1:5. Method for recovering rare earth metals.
17. The method of claim 1, wherein step e) converts cerium(IV) into cerium(III) using hydrogen peroxide as a reducing agent, and then strips the cerium(III) with an acid solution to obtain a cerium-containing acid solution. A method for recovering rare earth metals.
18. The method of claim 1, further comprising the step of f) recovering rare earth metals other than cerium from the raffinate.
19. The method of claim 17, further comprising recovering the cerium contained in the acid solution by precipitating it in the form of cerium oxalate using oxalate ions.
20. The method of claim 18, wherein step f) includes precipitating rare earth metals other than cerium in the raffinate in the form of oxalate using oxalate ions.

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